A. Setup Default Return Window
Go to Settings -> Returns -> Return Options section.
Scroll down to the -> Default Return Window. Here you'll be able to set a default return window between 0 - 364 days. Then you can set up the Return Window Start Date. Click over the Save button and the default return window will be applied as default to all Return Rules.
B. Setup Return Window for Individual Rules
Go to Settings -> Returns -> Return Policies section -> click on Edit.
Go to the Configuration section -> Return Window and here you'll be able to customize the Return Window for an individual rule. Then scroll down the page and click on Save.
Custom Return Window is useful when used in combination with various product tags.
Example: Your store might sell Mobile Phones as well as TV's your return window for Mobile Phones can be 15 days when the return window for TV's is 45.
As soon as the product is shipped the customer can easily see how many days left they have until they can return the product.
If the customer tries to return a product after the return period passed (eg. return window 30 days and the customer tries to return after 35 days) the customer will not be able to request a return for the product.
If you sell products that are non-returnable, simply set the return window to 0 days.
For a video walkthrough of configuring returns, please take a look at the video below.